9.6: Actions of insulin and glucagon in fat metabolism

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Learning Objectives

Summarize the relationship between insulin secretion and glucagon regulation in metabolism homeostasis between lipids and carbohydrates

Glucagon and insulin are peptide hormones secreted by the pancreas that play a key role in maintaining a stable blood glucose level and body homeostasis. Glucagon is produced by alpha cells in the pancreas and elevates the concentration of glucose in the blood by promoting gluconeogenesis and glycogenolysis. Glucose is stored in the liver in the form of the polysaccharide glycogen. Liver cells have glucagon receptors and when glucagon binds to the liver cells they convert glycogen into individual glucose molecules and release them into the bloodstream. As these stores become depleted, glucagon then encourages the liver and kidney to synthesize additional glucose by gluconeogenesis. Glucagon also turns off glycolysis in the liver, causing glycolytic intermediates to be shuttled to gluconeogenesis to produce glucose from fat.

Insulin is produced by beta cells in the pancreas and acts to oppose the functions of glucagon. Its main role is to promote the conversion of circulating glucose into glycogen via glycogenesis in the liver and muscle cells. Insulin also inhibits gluconeogenesis and promotes the storage of glucose in fat through lipid synthesis and also by inhibiting lipolysis and beta-oxidation of fatty acids.

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